A professor emeritus at Queen’s University in Kingston, Ont. — the former director of the Sudbury Neutrino Observatory in northern Ontario — is a co-winner of the 2015 Nobel Prize in Physics for his work on tiny particles known as neutrinos.

Arthur McDonald was roused from sleep at about 5 a.m. on Tuesday by a phone call from the Nobel Prize committee telling him the news.

“I was a little surprised,” he said in a telephone interview from Kingston, laughing with joy. “I am overwhelmed, but excited.”

The first thing the 72-year-old did as a Nobel Prize winner was hug his wife. “Thank you,” he told her. McDonald and Japanese scientist Takaaki Kajita were cited for the discovery of neutrino oscillations and their contributions to experiments showing that neutrinos change identities.

“We were also able to determine that neutrinos do have a small mass and that’s something that wasn’t known before and it helps to place neutrinos in the laws of physics at a very fundamental level,” McDonald said.

“So it’s very fundamental in terms of understandting how the world works at a very microscopic level.”

The Nobel Prize committee was impressed.

“The discovery has changed our understanding of the innermost workings of matter and can prove crucial to our view of the universe,” the Royal Swedish Academy of Sciences said in announcing the award early Tuesday.

Even McDonald’s colleagues were caught off guard by the announcement. By mid-day Tuesday, Tony Noble, a physicist at Queen’s University and associate director of the Sudbury Neutrino Observatory, said they were scrambling to put together a party to celebrate the big news.

“This is just incredible and it validates all the incredible work that is being done at the (neutrino lab in Sudbury),” Noble said.

McDonald said being named by the committee is a “very daunting experience, needless to say.”

“Fortunately, I have many colleagues as well who share this prize with me.”

McDonald said they have put in a “tremendous amount of work” and that he benefited from having a “very friendly collaboration among scientists from Canada, the United States, Britain and Portugal.”